The present invention relates to a dynamic memory, and more particularly to a dynamic random access memory having a built-in refresh address counter.
Dynamic random access memories (DRAM) are extensively used as a high speed, large capacity memory. The mainstream of DRAMs currently in use is of an address multiplex type. The address multiplex type DRAM is structured so that row address signals are taken in as an active level of a row address strobe signal (RAS) via a pair of address input terminals, and then column address signals are taken in as an active level of a column address strobe signal (CAS) via the same pair of address input terminals. This construction reduces the number of address terminals to one half and also reduces the size of package.
As one method of refreshing an address multiplex type DRAM is known where, contrary to the use of the row address strobe signal at the time of normal accessing as an active level and then using the column address strobe signal as an active level, the column address strobe signal is used first as an active level and then the row address strobe signal is used as an active level to refresh the memory cell of the row designated by the built-in refresh address counter as the internal refresh mode of the DRAM. This technique has been called as CAS Before RAS (CBR) refreshing and is now employed in large capacity DRAMs. In order to refresh all of the memory cells, a CBR refreshing operation must be repeated for all of the rows of a memory array.
With the prior art DRAM as mentioned above, the refreshing operation is carried out using a power source at a voltage level similar to that used during the normal accessing operation. This arrangement consumes a relatively large amount of power during the refreshing operation.
Also CBR refreshing requires a controlling operation by an external a unit to successively activate a column address strobe signal and then a row address strobe signal each time DRAM is in the CBR refreshing cycle. This complicates the control of the refreshing operation and thus lowers the operating efficiency.